Traditionally, brush seals have been provided in order to present a seal between two components. The brush seals essentially comprise bristles which extend from one component to another. Tip portions of each bristle contacting the other component in order to provide a seal. Such brush seals have two distinct disadvantages when presented with high differential pressures. Firstly, the bristles tend to wear rapidly and secondly, the bristles can be forced into a “locked” configuration where the bristles cannot move to accommodate excursions in the components to be sealed.
More recently the seal arrangements have been specified which relieve some of the disadvantages of brush seals. Leaf elements secured in a juxtaposed relationship replace the bristles of a brush seal. The leaf elements are compliant in a radial direction but stiff in an axial direction. In such circumstances, it is not necessary to provide a supportive backing ring as for bristles of a brush so removing the tendency for bristle seal elements to lock in position as pressure is applied. Unfortunately, such leaf seal elements are still liable to suffer from so-called “blow-down” behaviour if the pressure distribution above and below each leaf seal element is not balanced. In short, the ends of each leaf seal element rub hard onto its opposed component such as a rotating surface. In such circumstances, leaf seal elements continue to suffer from premature wear unless a balancing upward force is provided in the form of an air film between the leaf seal element tip edge and the opposed component surface e.g. rotating surface.
Previously, leaf seal elements have been provided as plain leafs. These leafs have an interleaf clearance provided by a spacing member in order to allow provision of an air film. This air film is caused by pressure in the spacing between leaf seal element. The air film is formed between leaf seal element tip edges and to the opposed component i.e. rotor. Alternatively, each seal element can be tapered from its mounting end in order to create spacing at the seal end and so the desired behaviour. Unfortunately, provision of either spacers between adjacent leaf seal elements or tapering of such leaf seal elements renders manufacture of a seal arrangement incorporating leaf seal elements difficult and the eventual seal arrangement is relatively inefficient and leaky in terms of seal effectiveness.